add a validation to prevent an inconsistent combination of values and tests for this validation

config/locales/en.yml

@@ -539,7 +539,7 @@ en:
       in_soft_max_range:
         message: "Net income is higher than expected based on the lead tenant’s working situation. Are you sure this is correct?"
     income:
-      under_soft_min_for_economic_status: 
+      under_soft_min_for_economic_status:
         title_text: "You told us income was %{income}."
         hint_text: "This is less than we would expect for someone in this working situation."
     rent:
@@ -571,10 +571,10 @@ en:
       hint_text: "This is higher than we would expect."
     shared_ownership_deposit:
       title_text: "You told us that the mortgage, deposit and discount add up to %{mortgage_deposit_and_discount_total}"
-    old_persons_shared_ownership: 
+    old_persons_shared_ownership:
       title_text: "You told us the buyer is using the Older Persons Shared Ownership scheme."
       hint_text: "At least one buyer must be aged 65 years and over to use this scheme."
-    staircase_bought_seems_high: 
+    staircase_bought_seems_high:
       title_text: "You told us that %{percentage}% was bought in this staircasing transaction."
       hint_text: "Most staircasing transactions are less than 50%"
     monthly_charges_over_soft_max: